Conservation grazing

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Conservation grazing is the use of semi-feral or domesticated grazing livestock to maintain and increase the biodiversity of natural or semi-natural grasslands, heathlands, wood pasture, wetlands and many other habitats.[1][2]

Also called targeted grazing when used to meet specific goals for rangeland,[3] conservation grazing is generally less intensive than practices such as prescribed burning,[2] but still needs to be managed to ensure that overgrazing does not occur. The practice has proven to be beneficial in moderation in restoring and maintaining grassland and heathland ecosystems. The optimal level of grazing will depend on the goal of conservation, and different levels of grazing, alongside other conservation practices, can be used to induce the desired results.[4]

History[edit]

For historic grasslands, grazing animals, herbivores, were a crucial part of the ecosystem. When grazers are removed, historically grazed lands may show a decline in both the density and the diversity of the vegetation. The history of the land may help ecologists and conservationists determine the best approach to a conservation project.[5]

Historic threats to grasslands primarily began with land conversion to crop fields. However, this threat shifted to improper land management techniques and more recently to the expansion of woody species of plants due to a lack of management and to climate change. These threats hinder the ecological importance of grassland communities. Grasslands are a carbon sink, and benefit livestock. Ecologically, if managed properly, conservation grazing can help to restore these historic ecological assets. However, if the grazing levels reach too high, shrubs will persist over grassland.[6]

In 1985, the US established the Conservation Reserve Program (CRP), which gave money to farmers to leave land fallow, instead of using it for crops or grazing. It was argued that exclusion or use of moderate grazing would be an important factor in future decisions as to what to do with the land that was a part of the CRP program. The land could have varied uses in the future. The minimization of the effects of climate change has a lot to do with the sequestering of carbon, and expansive grasslands may play an essential role in this process.[7] But also it could be used for the rotation of crops to the benefit of wildlife populations.[clarification needed]

Conservation grazing in practice[edit]

The use of conservation grazing is dependent on what type of ecosystem, habitat, and plant community are desired to be maintained or restored. Grazing is a beneficial tool used to create a grass and small shrub dominated area. Tasker and Bradstock[8] found that grazed areas returned a lower vegetation complexity score than ungrazed, however this was mainly because tree species and shrubs produce higher complexity scores than grasses – the grazed areas were composed primarily of bunch grasses and the ungrazed were dominated by shrub species. Certain areas that have been, historically, woody forest, may be chosen to be restored back to historical conditions, thus Tasker’s and Bradstock’s study would imply that wooded areas should remain ungrazed by livestock such as cattle.[original research?]

Conservation practices such as grazing need to be monitored closely. If they are not, the practice can become overused and have an opposite effect than intended. Overgrazing may cause erosion, habitat destruction, soil compaction, or reduced biodiversity (species richness).[9]

One issue of controversy with grazing is whether conservation grazing is in fact beneficial to a grassland community and what intensity of grazing management needs to be taken. Rambo and Faeth found that the use of vertebrates for grazing of an area would increase the species richness of plants by decreasing the abundance of dominant species and increasing the richness of rarer species. The decrease in abundance may lead to a more open forest canopy and more room for other plant species to emerge.[10]

Grazing restoration effect dependent on grazer species[edit]

Different grazing species have different effects. For example, elk and horses have a similar grazing frequency to cattle but tend to spread their zone of grazing to cover a greater area, producing a smaller effect on a given area than cattle would.[11] Similarly, cattle have been found to be more useful in the restoration of pastures with low species richness, and sheep were found useful for the re-establishment of neglected fields.[12] The type of area that needs to be restored or maintained will determine the species of grazer ideal for conservation grazing. Dumont et al.[13] found in the use of varied breeds of steers that “traditional breeds appeared slightly less selective than commercial breeds”, but did not make a significant difference in biodiversity. In this particular study biodiversity was maintained by the same amount by both breed types.

Effects on native and non-native plant species[edit]

Conservation grazing is a tool used for conserving biodiversity. However, one danger in grazing is the potential for invasive species to be enhanced as well as the native biodiversity. A study by Loeser et al. showed that areas of high intensity grazing and grazer removal increased the biomass of nonnative introduced species. Both showed that an intermediate approach is the best method. The nonnatives did demonstrate that they were not as well adapted to the disturbances, such as drought. This indicated that implementing controlled grazing methods would decrease the abundance of nonnatives in those plots that had not been properly managed.[14]

Effects of grazing can also depend on the individual plant species and its response to grazing. Plants that are adapted to extensive grazing (such as that done by cattle) will respond quicker and more effectively to grazing than native species that have not had to cope with intense grazing pressure in the past. An experiment done by Kimball and Schiffman showed that grazing increased the cover of some native species but did not decrease the cover of nonnative species. The species diversity of the native plants was able to respond to the grazing and increase diversity. The community would become denser than originally with the increased biodiversity. (However, this may have been simply variance in plots due to the fact that the native and nonnative compositions were of different species between the grazed and ungrazed plots.)[11]

Effects on non-plant species[edit]

Insects and butterflies[edit]

Degree of grazing has a significant effect on the species richness and abundance of insects in grasslands. Land management in the form of grazing tends to decrease diversity with increased intensity. Kruess and Tscharntke attribute this difference to the increased height of grasses in the ungrazed areas. The study showed that the abundance and diversity of insects (such as butterfly adults, trap-nesting bees and wasps) were increased by increased grass height. However, other insects such as grasshoppers responded better to heterogeneity of the vegetation.[15]

Vertebrates[edit]

Grazing can have varied effects on vertebrates. Kuhnert et al. observed that different bird species react in different ways to changes in grazing intensity.[16] Grazing has also been thought to decrease the abundance of vertebrates, such as the Prairie Dog and the Desert Tortoise. However, Kazmaier et al. found that the effect of moderate grazing on the Texas Tortoise did not show a significant difference when comparing grazed and ungrazed plots.[9]

Rabbits have been widely discussed due to their influences on land composition. Bell and Watson found that rabbits show grazing preference for different plant species.[17] This preference can alter the composition of a plant community.[18] In some cases, if the preference is for a non-native, invasive plant, rabbit grazing may benefit the community by reducing non-native abundance and creating room for the native plant species to fill.[19] When rabbits graze in moderation they can create a more complex ecosystem, by creating more variable environments that will allow for more predator-competitor relationships between the various organisms.[18] However, besides the effect on wild vegetation, rabbits destroy crops, compete with other herbivores, and can result in extreme ecological damage. Competition can be direct or indirect. The rabbits may specifically eat the competitions target food or it may inhibit the growth of grasses that other species eat. For example, rabbit grazing in the Netherlands inhibits tall grasses from becoming dominant. This in turn enhances the suitability of the pasture for Brent Goose. However, they may benefit predators that do better in open areas, because the rabbits reduce the amount of vegetation making it easier for those predators to spot their prey.[18]

Finally, grazing has demonstrated use in clearing dry brush to reduce the fire hazard of drought-striken areas.[20]

Effect on ephemeral wetland ecosystems[edit]

Ephemeral wetlands degradation and loss of biodiversity had, at one point in time, been blamed on mismanaged grazing of both native and non-native ungulates and other grazers. A study done by Jaymee Marty of The Nature Conservancy examined the effects on the vernal pools formed in California when grazers were removed.[21] The results of the short study showed that areas where grazers were removed had a lower diversity of native grasses, invertebrates and vertebrates in the pools, with an increase in non-native grass abundance and distribution in the area. The study also demonstrated reduced reproduction success of individual species in the area, such as the Western Spadefoot Toad and California Tiger Salamander. Marty argues that this decrease is due to ecosystems adapting to historical changes in grazers and the effects they have. In other words, the historic ecosystem, theoretically, would have responded positively to the removal of cattle grazing, however, the system has adapted to the European introduced species and now may require them for maintained diversity.[21] In another study performed by Pyke and Marty, measurements showed that on average, vernal ponds on grazed land pooled longer than ungrazed areas and soil was more resistant to water absorption in the grazed areas.[22]

See also[edit]

References[edit]

  1. ^ Conservation Grazing Peninsula Open Space Trust, California, US, 2009. (cited 2009 Mar 11)
  2. ^ a b What is Conservation Grazing? Grazing Advice Partnership, UK, 2009.
  3. ^ "Use Target Grazing To Take Aim At Invasive Weeds", Beef magazine, May 2007 
  4. ^ "Free-Range Landscaping Rent-a-goat.com and Others Bring in Herds to Trim the Yard, Get Rid of Weeds". Wall Street Journal. 
  5. ^ History distribution and challenges to bison recovery in the northern Chiuahuan desert Rurik, L., G. Ceballos, C. Curtin, P. J. P. Gogan, J. Pacheco, and J. Truett. Conservation Biology, 2007, 21(6): 1487-1494.
  6. ^ An ecosystem in transition: causes and consequences of the conversion of Mesic grassland to shrubland Briggs, J. M., A. K. Knapp, J. L. Heisler, J. M. Blair, M. S. Lett, G. A. Hoch and J. K. Mccarron. Bioscience, 2005, 55(3): 243-254.
  7. ^ Effects of grazing on restoration of southern mixed prairie soils Fuhlendorf, S.D., H. Zhang, T.R. Tunnel, D.M. Engle and A.F. Cross. Restoration Ecology, 2002, 10(2): 401-407.
  8. ^ Influence of cattle grazing practices on forest understory structure in North-eastern New South Wales Tasker, E M and R A Bradstock. Austral Ecology, 2006, 31(4): 490-502.
  9. ^ a b Effects of Grazing on the demography and growth of the Texas tortoise Kazmaier, R.T., E.C. Hellgren, D.C. Ruthven III, and D.K. Synatzske. Conservation Biology, 2002, 15(4): 1091-1101.
  10. ^ Effect of Vertebrate Grazing on Plant and Insect Community Structure Rambo, J.L and S.H. Faeth. Conservation Biology, 2001, 13(5): 1047-1054.
  11. ^ a b Differing Effects of Cattle Grazing on Native and Alien Plants Kimball, S. and P.M Schiffman. Conservation Biology, 2003, 17(6): 1681-1693.
  12. ^ Effects of livestock breed and grazing intensity on grazing systems: 3. Diversity of Vegetation Scimone, M., A.J. Rook, J.D. Gavel, and N. Sahin. Grass and Forage Science, 2007, 62(2): 172-184.
  13. ^ Effects of livestock breed and grazing intensity on biodiversity and production in grazing systems and diet selection: 2. Diet systems Dumont, B., A.J. Rook, Ch. Coran, and K.U. Rover. Grass and Forage Science, 2007, 62(2): 159-171.
  14. ^ Impact of grazing intensity during Drought in an Arizona Grassland Loeser, M R R, T D Sisk, and T E Creus. Conservation Biology, 2006, 21(1): 87-97.
  15. ^ Grazing Intensity and the Diversity of Grasshoppers, Butterflies, Trap-Nesting Bees and Wasps Kruess, A. and T. Tscharntke. Conservation Biology, 2002, 16(6): 1570-1580.
  16. ^ Assessing the Impacts of grazing levels on bird density in woodland habitat: a Bayesian approach using expert opinion Kuhnert, P.M, T.G. Martin, K. Mengersen, and H.P Possingham. Environmetrics, 2005, 16(7): 717-747.
  17. ^ Preferential grazing of five varieties of spring barley by wild rabbits (Oryctolagus cuniculus) Bell, A.C. and S. Watson. Annals of Applied Biology, 2008, 122(3): 637-641.
  18. ^ a b c Key role of European rabbits in the conservation of the Western Mediterranean Basin Hotspot Delibes-Mateos, M., M. Delibes, P. Ferreras, and R. Villafuerte. Conservation Biology, 2008, 22(5): 1106-1117.
  19. ^ The Effects of herbivory and competition on the invasive alien plant Senecio inaequidens (asteraceae) Scherber, C., M.J. Crawley and S. Povembshi. Diversity and Distributions, 2003, 9(6): 415-426.
  20. ^ "American Pastoral". Brown Alumni Monthly. Sept–Oct 2012. 
  21. ^ a b Effects of Cattle Grazing on Diversity in Ephemeral Wetlands Marty, J.T. Conservation Biology, 2005, 19(5): 1626-1632.
  22. ^ Cattle grazing Mediates Climate change impacts on Ephemeral Wetlands Pyke, C.R. and J. Marty. Conservation Biology, 2005, 19(5): 1619-1625.

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